Tundish Spray/Working lining.
1. Parking the tundish at spray stand by using cranes.
2. Checking the main electrical power supply and emergency switch of spray machine and ensuring flow start condition readiness is achieved.
3. Checking air valve condition and maintaining air pressure at 3 bar. Checking the water valve and ensuring water flow is at 1200 ltr/hr.
4. Lifting 1 MT spray mass bag with semi portal crane and placing it on bag slitter on spray machine hopper. Allowing the materials to get emptied in the hopper (Access to the hopper is prohibited as far as safety practices are concerned).
5. Before commencing with tundish spraying, ensuring the temperature of the tundish to be less than 100 deg C.
6. Spraying is to be done layer by layer. Building up layer less than 25 mm first and waiting for steam to evacuate, then spraying another so as to maintain sidewall thickness of 40 mm to 50 mm and bottom lining thickness from 50 to 60 mm.
7. Curing for 30 minutes to 1 hr at room temperature after the lining is set. After cooling at room temperatures heating is done for 4hours with the help of a dryer.
Heating schedules of spray mass or working lining
1. The tundish is heated from room temperature to 200-degree centigrade within 1hour
2. The temperature is further raised to 400-degree centigrade in the next one hour.
3. The temperature is held constant and soaked for the next one hour.
4. Then the tundish is simultaneously cooled for the next two hours.
SEN fixing for tundish with mono block stopper rod mechanism
1. Visual checking of SEN before fixing to ensure there is no damage or chipping off.
2. Mixing mortars with 3% water in semi-liquid condition. Appling mortar mix at the outer surface of the SEN neck area.
3. Inserting SEN into tundish well-block gently.
4. Checking the accuracy of SEN centering by jig. Equal distance between SENs is to be maintained.
5. Locking SEN by using low cement castable around the tundish well-block.
6. Sloping is done around the SEN.
7. The tundish cover is finally placed before shifting it to the caster area.
Tundish emergency gate preparation fixing and removal
1. After casting, used tundish is placed at the cooling stand for further cooling.
2. Removal of the emergency gate from tundish bottom.
3. Cleaning by weir brush, checking the screw and plate surface.
4. Checking liner and firing plate movement.
5. Placing the cylinder at its designated location and checking its position as well.
Heating Schedule for SEN
The inner wall temperature of 1000 degrees centigrade is to be reached within 30-40 minutes. Cracks can be generated for low preheating temperature whereas overheating of SEN causes oxidation and changes the material internal structure leading to crack formation as well. Thus the recommended inner wall temperature should be close to 1000 degrees centigrade and the SEN heating time should not be extended to more than 2hours.
Stopper rigging mechanism (SRM) fixing and removal.
1. After casting, used tundish is placed at the stand for cooling.
2. After cooling, removing the stopper pin from the SRM box and removing the mechanism from all strands by cranes and parking it on torque checking stand.
3. Cleaning all the debris or foreign materials from outside the box by hand brush.
4. Manual checking of hand wheel of SRM box.
5. Checking torque value for all mechanisms by the electrical testing unit in every cycle – fixing electrical plug with mechanism and ensuring that the unit power supply is in on condition. All the indicator lights should blink on the testing unit box and then the torque value is to be checked with the help of a pendant.
(Maximum torque value in upper position should be 2.2 and lower position should be 0.90. In case the torque value exceeds the maximum allowable limits the mechanism needs to be replaced with a new one. The mechanism is to be cleaned and greased after every 6 cycles).
1. Lifting the SRM mechanism by cranes and fixing it with tundish at the predefined position. The mechanism is tightened with the help of 30 mm ring spanner.
2. Fixing of stopper pin in MBS (monoblock stopper) with 34 mm side spanner for correct tightening of pin.
3. Lifting the MBS with the help of a crane and placing in every strand after tundish cover placement.
4. MBS with stopper pin is fixed with the mechanism extended arm and ensuring proper sitting of MBS on the SEN hole.
5. Protecting the stopper pin and mechanism arm with ceramic blanket.
6. Final inspection is done before dispatch to the casting platform to avoid any failures.
Recommended operating procedure.
- The recommended drying cycle at the tundish preparation bay and heating cycle at the caster needs to be followed for spray mass.
- Overheating at caster beyond 2 hr can damage spray mass and spray lining can fall or become weak due to prolonged heat at the caster. The burner flames at the heating stand should not impinge directly on the refractory lining. All heating stands should have a thermocouple arrangement.
- Slag to be controlled in the tundish as this might lead to excessive erosion as well as quality issues. If the slag level is high greater than 100 mm at any point of time, then the sequences to be restricted irrespective of life.
- Tundish level should not fall much below normal overflow or operating level during ladle change over and at normal operation. The tundish level should be maintained at a minimum of 85% of the total capacity. In case of tundish level falling to lower levels even for short durations, there are chances of spray mass falling with the slag crust and slag mixing with clean steel.
- Ladle shroud verticality should be ensured so that it is centered over the tundish flow modifier. The steel stream from the shroud should not hit the tundish wall. In case, ladle-free opening is not happening at the beginning of the heat, there will be chances of working lining damage due to splashes from the initial unshrouded open stream.
- Top lancing in tundish is not recommended.
- Excessive ladle slag carry over to be avoided as mentioned earlier.
- The recommended surface temperature for spray mass application is 80 -100 deg C which needs to be maintained – deviation from these limits will affect spray mass application quality.
- Proper tundish slag chemistry is vital for the performance of working lining and FeO and MnO level is to be minimized in the slag.
Heating Schedule at Caster
The tundish is to be heated to 1000 degrees centigrade within half an hour and then raised to 1200 degrees centigrade within the next 2 hrs and the recommended total tundish heating time is 2.5 hrs (approx.)
